Nitride semiconductor light-emitting element

Abstract

To provide a technique of improving the efficiency of injecting holes into an active layer in a large-output nitride semiconductor light-emitting element which supplies large currents and emits light.SOLUTION: A nitride semiconductor light-emitting element 1 includes: a double quantum well active layer 13; a p-side AlGaN guide layer 14 laminated on a front surface side of the double quantum well active layer 13; and an electronic block layer 15 laminated on a front surface side of the p-side AlGaN guide layer 14. The p-side AlGaN guide layer 14 has a composition flat layer 14A in which an Al composition is the same in a lamination direction D and a composition inclination layer 14B in which the Al composition is inclined in the lamination direction D.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to a nitride semiconductor light emitting device. [Background technology]

[0002] Patent Document 1 discloses a technique for improving the efficiency of hole injection into an active layer by sandwiching the active layer between composition gradient layers in which the Al composition is gradient in the stacking direction. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2015-2324 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, in a high-output nitride semiconductor light-emitting device that emits light by supplying a large current, there is room for improvement in technology for increasing the efficiency of hole injection into the active layer.

[0005] The present invention has been made in view of the above-mentioned conventional circumstances, and aims to provide a technique for increasing the efficiency of hole injection into an active layer in a high-output nitride semiconductor light-emitting device that emits light by supplying a large current. Here, a large current is defined as approximately 1 kA / cm 2 The current is as above. [Means for solving the problem]

[0006] The nitride semiconductor light-emitting device of the present invention comprises: An active layer; A guide layer laminated on a surface side of the active layer; an electron blocking layer laminated on a surface side of the guide layer; Equipped with The guide layer includes a flat composition layer having a constant Al composition in the stacking direction, and a gradient composition layer having an Al composition that is gradient in the stacking direction.

[0007] By configuring the guide layer with a flat composition layer and a gradient composition layer, it is easy to increase the efficiency of carrier injection into the active layer in a high-output nitride semiconductor light-emitting device that emits light by supplying a large current. Hereinafter, the term "carrier injection efficiency" will be used to indicate the efficiency of carrier injection into the active layer. [Brief description of the drawings]

[0008] [Figure 1] 1 is a schematic diagram showing a nitride semiconductor light emitting device. [Diagram 2] 1 is a graph showing the Al composition in the stacking direction in a nitride semiconductor light emitting device. [Diagram 3] 1 is a graph showing the relationship between the thickness of a compositionally graded layer and the carrier injection efficiency. [Figure 4] 1 is a graph showing the relationship between the thickness of a compositionally flat layer and the carrier injection efficiency. [Diagram 5] 1 is a graph showing the relationship between the distance between an AlGaN quantum well layer and a compositionally graded layer and carrier injection efficiency. [Figure 6] 1 is a graph showing the relationship between the difference in Al composition between the electron blocking layer side and the flat composition layer side in a composition gradient layer, and the carrier injection efficiency. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] A preferred embodiment of the present invention will now be described.

[0010] The compositionally graded layer may be laminated on the surface of the flat composition layer, and the electron blocking layer may be laminated on the surface of the compositionally graded layer. In this case, by laminating the electron blocking layer on the compositionally graded layer, the difference in Al composition at the interface between the guide layer and the electron blocking layer becomes large, and the electron blocking effect of the electron blocking layer can be improved.

[0011] The Al composition of the compositionally graded layer can decrease with increasing distance from the flat-composition layer in the stacking direction. In this case, the amount of negative polarization charge can be made greater than the amount of positive polarization charge throughout the compositionally graded layer in the stacking direction, and the layer can exert an effect of attracting holes from other locations.

[0012] The thickness of the composition gradient layer in the stacking direction may be 1 nm to 30 nm, which is the most efficient way to increase the carrier injection efficiency.

[0013] The minimum value of the Al composition of the compositionally graded layer in the stacking direction may be equal to or greater than the minimum value of the Al composition of the active layer, thereby reducing the probability of carrier recombination in the compositionally graded layer and preventing carrier recombination in the active layer.

[0014] In the compositionally graded layer, the difference between the Al composition at the interface on the flat composition layer side and the Al composition at the interface on the electron blocking layer side can be 0.05 to 0.17, which can effectively suppress the rate of carrier recombination in the compositionally graded layer and increase the rate of carrier recombination in the active layer.

[0015] <Example 1> 1, the nitride semiconductor light-emitting device 1 of Example 1 includes a sapphire substrate S, an AlN layer 9, a u-AlGaN layer 10, an n-AlGaN cladding layer 11, an n-side AlGaN guide layer 12, a double quantum well active layer 13 as an active layer, a p-side AlGaN guide layer 14 as a guide layer, an electron blocking layer 15, a p-AlGaN cladding layer 16, and a p-GaN layer 17. The nitride semiconductor light-emitting device 1 is manufactured by stacking and growing the above layers from the front surface side (the upper side in FIG. 1, the same applies below) of the sapphire substrate S (hereinafter also referred to as substrate S) upward in the stacking direction D using a method such as metal-organic chemical vapor deposition (MOCVD) method.

[0016] The surface of the substrate S is the c-plane ((0001) plane). The AlN layer 9 has a thickness of, for example, 2 μm. The u-AlGaN layer 10 has a thickness of, for example, 5000 nm and an Al composition of 0.68.

[0017] The n-AlGaN cladding layer 11 is doped with Si as an n-type dopant. The concentration of Si in the n-AlGaN cladding layer 11 is 6×10 18 cm -3 2, the thickness of the n-AlGaN cladding layer 11 is 4000 nm. The Al composition of the n-AlGaN cladding layer 11 is 0.62, and the Ga composition is 0.38.

[0018] No dopant is added to the n-side AlGaN guide layer 12. The thickness of the n-side AlGaN guide layer 12 is 50 nm. The Al composition of the n-side AlGaN guide layer 12 is 0.45, and the Ga composition is 0.55.

[0019] The double quantum well active layer 13 is formed by sandwiching one AlGaN barrier layer 13B between two AlGaN quantum well layers 13A in the stacking direction D. The AlGaN quantum well layer 13A has a thickness of 2.5 nm, an Al composition of 0.35, and a Ga composition of 0.65. The AlGaN barrier layer 13B has a thickness of 10 nm, an Al composition of 0.45, and a Ga composition of 0.55.

[0020] The p-side AlGaN guide layer 14 has a flat-composition layer 14A and a graded-composition layer 14B. The flat-composition layer 14A is stacked on the surface of the double quantum well active layer 13. The flat-composition layer 14A has a thickness of 40 nm. The flat-composition layer 14A has an Al composition of 0.5 and a Ga composition of 0.5. The flat-composition layer 14A has a constant Al composition in the stacking direction D.

[0021] The compositionally graded layer 14B is laminated on the surface of the compositionally flat layer 14A. The thickness of the compositionally graded layer 14B is 10 nm. The compositionally graded layer 14B has an Al composition that decreases upward in the stacking direction D. Specifically, the Al composition at the interface of the compositionally graded layer 14B with the compositionally flat layer 14A is 0.5, and the Ga composition is 0.5. The Al composition at the interface of the compositionally graded layer 14B away from the compositionally flat layer 14A is 0.4, and the Ga composition is 0.6. The compositionally graded layer 14B has a composition that decreases at a constant rate from 0.5 to 0.4 as it moves away from the compositionally flat layer 14A upward in the stacking direction D.

[0022] The electron blocking layer 15 has a thickness of 10 nm. The electron blocking layer 15 has an Al composition of 0.92 and a Ga composition of 0.08. The electron blocking layer 15 is laminated on the surface of the p-side AlGaN guide layer 14. Specifically, the electron blocking layer 15 is laminated on the surface of the compositionally graded layer 14B.

[0023] The p-AlGaN cladding layer 16 includes a first cladding layer 16A and a second cladding layer 16B. The first cladding layer 16A is laminated on the surface of the electron blocking layer 15. The thickness of the first cladding layer 16A is 320 nm. The Al composition of the interface of the first cladding layer 16A with the electron blocking layer 15 is 0.82, and the Ga composition is 0.18. The Al composition of the interface of the first cladding layer 16A on the side away from the electron blocking layer 15 is 0.6, and the Ga composition is 0.4. The first cladding layer 16A has a composition gradient such that the Al composition decreases at a constant rate from 0.82 to 0.6 as it moves away from the electron blocking layer 15 upward in the stacking direction D.

[0024] The second cladding layer 16B is laminated on the first cladding layer 16A. The thickness of the second cladding layer 16B is 75 nm. The Al composition at the interface with the first cladding layer 16A in the second cladding layer 16B is 0.6, and the Ga composition is 0.4. The Al composition at the interface away from the first cladding layer 16A in the second cladding layer 16B is 0, and the Ga composition is 1.0. The second cladding layer 16B has a composition gradient such that the Al composition decreases at a constant rate from 0.6 to 0 as it moves away from the first cladding layer 16A upward in the lamination direction D.

[0025] The thickness of the p-GaN layer 17 is 10 nm. The p-GaN layer 17 is doped with Mg as a p-type dopant.

[0026] [Verification of the p-side AlGaN guide layer] Next, the change in carrier injection efficiency was simulated when the thickness of the p-side AlGaN guide layer 14 was fixed at 50 nm and the thickness of the compositionally graded layer 14B was changed. The following simulations were performed using software SiLENSe Laser Edition (manufactured by STR Japan Co., Ltd.). Specifically, the thickness of the compositionally graded layer 14B was changed to eight types, 1 nm, 2 nm, 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, and 50 nm, and the carrier injection efficiency was simulated for each of these thicknesses. The Al composition of the compositionally graded layer 14B at the interface with the compositionally flat layer 14A was 0.5, and the Al composition of the compositionally graded layer 14B at the interface away from the compositionally flat layer 14A was 0.4.

[0027] As shown in Fig. 3, when the thickness of the compositionally graded layer 14B is 1 nm to 20 nm, the carrier injection efficiency is found to be greater than 45%. This value is greater than the carrier injection efficiency (40%, indicated by the dotted line in Fig. 3) when the entire p-side AlGaN guide layer 14 is the flat composition layer 14A. Also, when the thickness of the compositionally graded layer 14B is 5 nm to 20 nm, the carrier injection efficiency is found to exceed 50%. And, when the thickness of the compositionally graded layer 14B is 30 nm, the carrier injection efficiency is found to be approximately 45%.

[0028] It was found that when the thickness of the compositionally graded layer 14B is 30 nm or more, the carrier injection efficiency becomes less than 45%, approaching the carrier injection efficiency (40%) when the entire p-side AlGaN guide layer 14 is the compositionally flat layer 14A. This is believed to be because when the thickness of the compositionally graded layer 14B is 30 nm or more, the rate of carrier recombination at the interface between the p-side AlGaN guide layer 14 and the electron block layer 15 increases, thereby reducing the carrier injection efficiency in the double quantum well active layer 13. Therefore, the thickness of the compositionally graded layer 14B in the stacking direction D is preferably 1 nm to 30 nm, and more preferably 5 nm to 20 nm.

[0029] Next, the change in carrier injection efficiency was simulated when the thickness of the compositionally flat layer 14A was changed while the thickness of the compositionally flat layer 14B was fixed at 10 nm. Specifically, the thickness of the compositionally flat layer 14A was changed to six types, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, and 90 nm, and the carrier injection efficiency was simulated for each of them. In addition, the carrier injection efficiency was also simulated when the thickness of the compositionally flat layer 14A was 80 nm and the thickness of the compositionally flat layer 14B was 20 nm.

[0030] As shown in Fig. 4, it was found that the carrier injection efficiency remains constant at a value greater than 51% even when the thickness of the compositionally flat layer 14A is changed. It was also found that the carrier injection efficiency decreases when the thickness of the compositionally flat layer 14A is 80 nm and the thickness of the compositionally graded layer 14B is 20 nm. In other words, it is believed that when the compositionally graded layer 14B is made thicker, the probability of carriers recombining in the compositionally graded layer 14B increases, and as a result, the carrier injection efficiency in the double quantum well active layer 13 decreases.

[0031] Next, a simulation was performed to determine the change in carrier injection efficiency when the thickness of the p-side AlGaN guide layer 14 was fixed at 50 nm, the thickness of the compositionally graded layer 14B was fixed at 10 nm, and the position of the compositionally graded layer 14B was changed in the stacking direction D within the p-side AlGaN guide layer 14. Specifically, the distance between the compositionally graded layer 14B and the upper AlGaN quantum well layer 13A was changed to six values, namely, 0 nm, 10 nm, 20 nm, 30 nm, 35 nm, and 40 nm, and the carrier injection efficiency was simulated for each of these values.

[0032] 5, it was found that the carrier injection efficiency exceeds 50% when the distance between the compositional gradient layer 14B and the upper AlGaN quantum well layer 13A is maximized (i.e., the compositional gradient layer 14B is adjacent to the electron block layer 15 in the stacking direction D). It was also found that the carrier injection efficiency is less than 45% when the distance between the compositional gradient layer 14B and the upper AlGaN quantum well layer 13A is 0 nm to 35 nm. This is because the difference in Al composition at the interface between the p-side AlGaN guide layer 14 and the electron block layer 15 increases by placing the compositional gradient layer 14B adjacent to the electron block layer 15 in the stacking direction D, and the electron blocking effect of the electron block layer 15 is enhanced.

[0033] Next, a simulation was performed to examine the change in carrier injection efficiency when the Al composition of the composition gradient layer 14B at the interface with the electron blocking layer 15 was changed. Specifically, the Al composition of the composition gradient layer 14B at the interface with the electron blocking layer 15 was changed to seven different values, namely, 0.5, 0.45, 0.4, 0.38, 0.35, 0.33, and 0.3, and the carrier injection efficiency was simulated for each of these values.

[0034] Here, the Al composition of the compositionally graded layer 14B at the interface on the flat-composition layer 14A side (hereinafter also referred to as the Al composition on the flat-composition layer 14A side) is 0.5. When the Al composition of the compositionally graded layer 14B at the interface on the electron block layer 15 side (hereinafter also referred to as the Al composition on the electron block layer 15 side) is 0.5, the difference between the Al composition (0.5) on the electron block layer 15 side and the Al composition (0.5) on the flat-composition layer 14A side in the compositionally graded layer 14B is 0.

[0035] Furthermore, when the Al composition on the electron blocking layer 15 side is 0.45, the difference between the Al composition (0.45) on the electron blocking layer 15 side and the Al composition (0.5) on the flat composition layer 14A side in the composition gradient layer 14B is 0.05.

[0036] Furthermore, when the Al composition on the electron blocking layer 15 side is 0.4, the difference between the Al composition (0.4) on the electron blocking layer 15 side and the Al composition (0.5) on the flat composition layer 14A side in the composition gradient layer 14B is 0.1.

[0037] Furthermore, when the Al composition on the electron blocking layer 15 side is 0.38, the difference between the Al composition (0.38) on the electron blocking layer 15 side and the Al composition (0.5) on the flat-composition layer 14A side in the composition gradient layer 14B is 0.12.

[0038] Furthermore, when the Al composition on the electron blocking layer 15 side is 0.35, the difference between the Al composition (0.35) on the electron blocking layer 15 side and the Al composition (0.5) on the flat-composition layer 14A side in the composition gradient layer 14B is 0.15.

[0039] Furthermore, when the Al composition on the electron blocking layer 15 side is 0.33, the difference between the Al composition (0.33) on the electron blocking layer 15 side and the Al composition (0.5) on the flat composition layer 14A side in the composition gradient layer 14B is 0.17.

[0040] When the Al composition on the electron blocking layer 15 side is 0.3, the difference between the Al composition (0.3) on the electron blocking layer 15 side and the Al composition (0.5) on the flat composition layer 14A side in the composition gradient layer 14B is 0.2.

[0041] As shown in Fig. 6, the carrier injection efficiency increases as the Al composition of the composition gradient layer 14B at the interface on the electron blocking layer 15 side decreases from 0.5 (i.e., the degree of composition gradient of the Al composition in the composition gradient layer 14B increases). The carrier injection efficiency decreases as the Al composition of the composition gradient layer 14B at the interface on the electron blocking layer 15 side approaches 0.3. In other words, the carrier injection efficiency changes in a bow shape as the Al composition of the composition gradient layer 14B at the interface on the electron blocking layer 15 side changes from 0.5 to 0.3. It was found that the carrier injection efficiency exceeds 50% and is maximized when the Al composition of the composition gradient layer 14B at the interface on the electron blocking layer 15 side is 0.4 to 0.35.

[0042] This is because the effect of generating positive charges (holes) by polarization doping increases as the degree of composition gradient of the Al composition of the composition gradient layer 14B increases, but if the Al composition of the composition gradient layer 14B at the interface on the electron block layer 15 side is made smaller than the Al composition (0.35) of the AlGaN quantum well layer 13A, the rate of carrier recombination at the interface between the electron block layer 15 and the composition gradient layer 14B increases, and the carrier injection efficiency is thought to decrease. For this reason, it is preferable that the Al composition of the composition gradient layer 14B at the interface on the electron block layer 15 side is equal to or greater than the Al composition of the AlGaN quantum well layer 13A. In other words, it is preferable that the minimum value of the Al composition of the composition gradient layer 14B in the stacking direction D is equal to or greater than the minimum value of the Al composition of the double quantum well active layer 13 (the Al composition of the AlGaN quantum well layer 13A).

[0043] Furthermore, the minimum value of the Al composition of the composition-graded layer 14B in the stacking direction D is preferably smaller than the maximum value of the Al composition (the Al composition in the AlGaN barrier layer 13B) of the double quantum well active layer 13. Furthermore, in the composition-graded layer 14B, the difference between the Al composition at the interface on the composition flat layer 14A side and the Al composition at the interface on the electron blocking layer 15 side is preferably 0.05 to 0.17, and more preferably 0.1 to 0.15.

[0044] As described above, it has been found that the carrier injection efficiency can be increased by configuring the p-side AlGaN guide layer 14 with the flat-composition layer 14A having a constant Al composition in the stacking direction D, and the composition-graded layer 14B adjacent to the electron block layer 15 and having a composition gradient such that the Al composition gradually decreases upward in the stacking direction D. Specifically, it has been found that it is effective for the composition-graded layer 14B to have a thickness of less than 30 nm and an Al composition equal to or greater than the Al composition of the AlGaN quantum well layer 13A.

[0045] Next, the effects of the above embodiment will be described.

[0046] The nitride semiconductor light-emitting device 1 includes a double quantum well active layer 13, a p-side AlGaN guide layer 14 laminated on the surface of the double quantum well active layer 13, and an electron blocking layer 15 laminated on the surface of the p-side AlGaN guide layer 14, and the p-side AlGaN guide layer 14 has a flat composition layer 14A having a constant Al composition in the lamination direction D, and a graded composition layer 14B having a graded Al composition in the lamination direction D. According to this configuration, by forming the p-side AlGaN guide layer 14 from the flat composition layer 14A and the graded composition layer 14B, it is possible to increase the efficiency of carrier injection into the double quantum well active layer 13 in the high-output nitride semiconductor light-emitting device 1 that emits light by supplying a large current.

[0047] The compositionally graded layer 14B is laminated on the surface of the flat-composition layer 14A, and the electron blocking layer 15 is laminated on the surface of the compositionally graded layer 14B. With this configuration, by laminating the electron blocking layer 15 on the compositionally graded layer 14B, the difference in Al composition at the interface between the p-side AlGaN guide layer 14 and the electron blocking layer 15 becomes large, and the effect of blocking electrons by the electron blocking layer 15 can be improved.

[0048] The Al composition of the composition gradient layer 14B decreases with increasing distance from the composition flat layer 14A in the upward stacking direction D. For this reason, the amount of polarized negative charge can be made greater than the amount of polarized positive charge throughout the composition gradient layer 14B in the stacking direction D, and the layer can exert an effect of attracting holes from other locations.

[0049] The thickness of the compositionally graded layer 14B in the stacking direction D is 1 nm to 30 nm. With this configuration, the carrier injection efficiency can be most efficiently increased.

[0050] The minimum value of the Al composition of the composition-graded layer 14B in the stacking direction D is larger than the minimum value of the Al composition of the double quantum well active layer 13. With this configuration, it is possible to reduce the probability of carrier recombination in the composition-graded layer 14B and not inhibit the recombination of carriers in the double quantum well active layer 13.

[0051] In the compositionally graded layer 14B, the difference in Al composition between the interface on the flat-composition layer 14A side and the interface on the electron block layer 15 side is 0.05 to 0.17. This makes it possible to effectively suppress the rate of carrier recombination in the compositionally graded layer 14B and to increase the rate of carrier recombination in the double quantum well active layer 13.

[0052] The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is not limited to the embodiments disclosed herein, but is indicated by the claims, and is intended to include all modifications within the meaning and scope of the claims. (1) Unlike the first embodiment, the numbers of AlGaN quantum well layers and AlGaN barrier layers are not limited to those in the first embodiment. (2) The present invention may be applied not only to nitride semiconductor laser elements, but also to light emitting diodes and the like. (3) Unlike the first embodiment, an AlN layer may be laminated on another substrate such as an AlN substrate for crystal growth. (4) Unlike the first embodiment, Ge, Te, etc. may be used as an n-type dopant, and Zn, Be, Ca, Sr, Ba, etc. may be used as a p-type dopant. (5) Unlike the first embodiment, the nitride semiconductor light emitting device may be manufactured by MBE (molecular beam epitaxy). (6) Unlike Example 1, a layer having a composition different from those of the active layer and the guide layer may be laminated between the active layer and the guide layer, and a layer having a composition different from those of the guide layer and the electron blocking layer may be laminated between the guide layer and the electron blocking layer. (7) Unlike Example 1, the minimum value of the Al composition of the composition-graded layer in the stacking direction may be the same as the minimum value of the Al composition of the double quantum well active layer. In other words, the minimum value of the Al composition of the composition-graded layer in the stacking direction may be equal to or greater than the minimum value of the Al composition of the double quantum well active layer. [Explanation of symbols]

[0053] 1. Nitride semiconductor light emitting device 13 ... Double quantum well active layer (active layer) 14 ... p-side AlGaN guide layer (guide layer) 14A…composition flat layer 14B...composition gradient layer 15...Electron block layer D …Layer direction

Claims

1. An active layer; A guide layer laminated on a surface side of the active layer; an electron blocking layer laminated on a surface side of the guide layer; Equipped with The guide layer includes a flat composition layer having a constant Al composition in a stacking direction, and a composition gradient layer having an Al composition gradient in the stacking direction.

2. the compositionally graded layer is laminated on a surface of the compositionally flat layer, The nitride semiconductor light-emitting device according to claim 1 , wherein the electron blocking layer is laminated on a surface of the compositionally graded layer.

3. The nitride semiconductor light emitting device according to claim 2 , wherein the Al composition of said compositionally graded layer decreases with increasing distance from said compositionally flat layer in said stacking direction.

4. The nitride semiconductor light emitting device according to claim 3 , wherein the thickness of said composition gradient layer in said stacking direction is 1 nm to 30 nm.

5. 5 . The nitride semiconductor light emitting device according to claim 1 , wherein the minimum value of the Al composition of the composition gradient layer in the stacking direction is equal to or greater than the minimum value of the Al composition of the active layer.

6. 5. The nitride semiconductor light-emitting device according to claim 2, wherein in the composition gradient layer, a difference between the Al composition at an interface on the flat composition layer side and the Al composition at an interface on the electron blocking layer side is 0.05 to 0.17.

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